A number of cathode materials for Li-ion batteries are capable of providing very high capacity when charged to voltages greater than the standard 4.2 V vs. lithium metal. For many cathode materials, the higher the charging cut-off voltage, the more lithium that can be removed from the cathode material per unit weight. Unfortunately many cathode materials in these high states of charge can be reactive towards the electrolyte, resulting in surface reactions that can damage the cathode material and consume the electrolyte. This results in accelerated capacity loss and impedance build-up, greatly shortening the life of a Li-ion cell using these materials at such high voltages. Thus it is desirable to provide high voltage capable cathode materials that are stabilized to the electrolyte at high voltages to enable the construction of long life, very high capacity, high voltage Li-ion cells. One approach to improve the stability of these materials is to coat the surface of the active cathode materials with a phase that is more stable to the electrolyte at high voltages.
Some cathode materials have been reported with improved stability to the electrolyte at high voltages (>4.5V). For example, layered type Li1+y(NiCoMn)O2 (0=<y=<0.3) materials (for example U.S. Pat. No. 6,677,082 B2) coated or treated with AlF3 have demonstrated improved stability and life at high voltages. However, these coating layers may be insulating and not lithium ion conductive and may negatively affect the performance of the cathode material. Thus a high capacity, long cycle life cathode material that is stabilized at high voltages is highly desirable.